Let \(z_1, z_2\) be two complex numbers such that \(\bar{z}_1-i \bar{z}_2=0\) and \(\arg \left(z_1…

Let \(z_1, z_2\) be two complex numbers such that \(\bar{z}_1-i \bar{z}_2=0\) and \(\arg \left(z_1 z_2\right)=\frac{3 \pi}{4}\), then \(\arg \left(z_1\right)=\)
  1. \(\frac{\pi}{4}\)
  2. \(\frac{-\pi}{8}\)
  3. \(\frac{\pi}{8}\)
  4. \(\frac{\pi}{3}\)

Solution

Given \(\bar{z}_1-i \bar{z}_2=0\) \(\begin{array}{ll} \Rightarrow & \bar{z}_1=i \bar{z}_2 \\ \Rightarrow & \bar{z}_1=\overline{i z_2} \\ \Rightarrow & z_1=-i z_2 \end{array}\) Clearly argument of \(z_1=\) argument of \(z_2-\frac{\pi}{2}\) or argument \(z_1=\) argument \(z_2-\frac{\pi}{2}\) \(\Rightarrow\) argument \(z_2=\operatorname{argument} z_1+\frac{\pi}{2}\) Let argument \(z_1=\alpha\) Then, given argument \(\left(z_1 z_2\right)=\frac{3 \pi}{4}\) \(\Rightarrow\) argument \(z_1+\operatorname{argument} z_2=\frac{3 \pi}{4}\) \(\begin{aligned} \alpha+\alpha+\frac{\pi}{2} & =\frac{3 \pi}{4} \\ 2 \alpha & =\frac{3 \pi}{4}-\frac{\pi}{2} \Rightarrow \alpha=\frac{\pi}{8} \end{aligned}\)

Asked in: AP EAMCET 2020 (17 Sep Shift 2)

Practice more Complex Number questions on Aicharya